<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    hello world
</body>
<script>
    var a = 1;
    var b = 2;
    console.log(a, b);

    function fn() {
        var a = 10;
        var b = 20;

        // window["a"]
        window.a = 1000;
        window.b = 2000;


        console.log(a, b);
    }

    fn();



</script>

</html>